New eyes for the HESS experience
The cameras of the first four telescopes of the HESS Observatory in Namibia have seen their light collectors become more efficient and their reading electronics are rejuvenated by more than 15 years in order to reach the fifth telescope much more Large, installed in 2012. This upgrade will enable the five telescopes to work together and optimize the identification of the high-energy photons of the cosmos.
The commissioning of these cameras to the performance and reliability improved, using technology similar to that of the future Cherenkov Telescope Array (CTA) Suggests new scientific results for HESS The four cameras installed at the end of 2003 in Namibia were at the origin of numerous discoveries in high energy astrophysics. However, these four cameras, based on old technology developed in the 1990s, became difficult to maintain and had a time died high (several hundred microseconds) that disrupted the operation network with the camera’s large telescope installed in 2012, Equipped with a newer electronics with low dead time.
The dead time corresponds to the processing time of an event during which it is impossible to Record a new event. In order to optimally operate the 5 networked telescopes, it is essential that their dead time is of the same order of magnitude, otherwise the overall dead time will be defined by the least efficient element.
In addition to the necessary replacement of the Electronics of the cameras of the first four telescopes of HESS by a new electronics using the chip, a significant improvement concerned the effectiveness of the light collectors of the cameras. Indeed, the telescopes of the HESS observatory use light collectors or Winston cone. These collectors are used to concentrate the light of a large surface on a smaller photomultiplier and must in particular make it possible to reduce the noise due to the parasitic light reflected by the ground around the telescope.
The new collectors use a more reflective coating, developed for CTA, and thus allow almost 30% more light to be collected from the start. These new generation light collectors were produced by a 120-person SME located in Grasse, with which HESS maintains a long and fruitful collaboration. This company is specialized in the manufacture of optical polymer components. It is positioned on three sectors of activity face protection components for industrial applications and ultra precision machining. The habit of managing large productions enabled to carry out this manufacture of 6500 collectors in a few months.
The renovation of the cameras at the HESS site in Namibia was completed in September 2016 and the telescopes were ready for observation since December 2016. On 4 January 2017, the first signals of a cosmic particle accelerator were detected. The new cameras have recorded signals from the active nucleus of the galaxy 421, located 400 million light years in the constellation of the Great Bear. The simultaneous recording of the images of the incident particles by the 4 refurbished telescopes proceeded smoothly and the gamma source was finally detected, Thus demonstrating correct operation of the new cameras in stereoscopic mode. After four years of development, testing, production and deployment, this renovation is the final phase of the HESS This success is an important test for the next-generation gamma-ray observatory, CTA, which will use a similar camera technology. Designed as a new generation observatory CTA will increase the sensitivity by an order of magnitude compared to current telescopes, improve the angular resolution by a factor of extend the energy range by about 20 GeV up to several hundred TeV.